Doctors Explain How to Tell the Difference Between Food Poisoning and the Stomach Flu

The good news is that most cases of both the stomach flu and food poisoning only last a few days. Additionally, both the stomach flu and food poisoning can generally be managed at home. However, certain symptoms, along with factors like age and underlying health conditions, may make a medical visit necessary.

Here’s what doctors say about the differences between the stomach flu and food poisoning, and what to do if someone in your household is dealing with either condition.

Food poisoning vs stomach flu: What’s the difference?

Food poisoning definition

Simply put, “food poisoning is an illness caused by consuming spoiled and contaminated foods, or foods contaminated with toxins,” says Christine Lee, M.D., a gastroenterologist at Cleveland Clinic. The source of this contamination can be hard to pinpoint, as there’s a huge range of bacteria and viruses—say, like E. coli, listeria, salmonella, norovirus, and many more—that can lead to food poisoning in different ways. (See a full list here.)

“Foods can get contaminated at any point of processing (inadequate washing or refrigeration), production (incorrectly handled or undercooked), or during serving process (temperature and how it was served),” says Dr. Lee. It’s more common to experience food poisoning after eating in places where meals were prepared for large groups of people, such as school cafeterias, social gatherings, and restaurants, according to the National Institutes of Health.

Stomach flu definition

Stomach flu, medically known as viral gastroenteritis, “is a short-lived stomach disorder of an infectious cause attributed to a virus—most commonly noroviruses and rotavirus,” says Dr. Lee.

While rotavirus affects mostly children, norovirus is actually the leading cause of both stomach flu and foodborne illness in the United States, according to the Centers of Disease Control and Prevention. It is incredibly contagious and is typically spread among people in confined spaces, such as family homes, living communities, and cruise ships. This happens when an infected person does not thoroughly wash his or hands, touches surfaces used by other people, prepares food for other people, or shakes hands with another person.

While any sign of the “flu” can be alarming, stomach flu and influenza—which you should get vaccinated for every year—are not the same thing, explains Stephen Hanauer, MD, medical director of the Digestive Health Center at Northwestern Memorial Hospital. Influenza is a virus that attacks your respiratory system and getting a flu shot will not prevent stomach flu. The name “stomach flu” is also misleading, because the virus infects and attacks your intestines, not your actual stomach.

Food poisoning vs stomach flu symptoms

Because food poisoning and stomach flu have such similar symptoms, it can be tricky to figure out which one you’re dealing with.

Food poisoning symptoms

• Upset stomach
• Stomach cramps
• Nausea
• Vomiting
• Diarrhea
• Fever

Stomach flu symptoms

• Diarrhea
• Stomach pain and cramping
• Nausea
• Vomiting
• Sometimes fever
• Fatigue
• Extreme thirst (if dehydrated)
• Lightheadedness
• Headache or body aches

“Both may present with nausea, vomiting, diarrhea, abdominal pains, and a low-grade fever,” says Dr. Lee. However, stomach flu tends to involve more nausea and vomiting, while food poisoning may lead to more diarrhea.

“Bacterial food poisoning affects more of the colon, not small intestines, which causes the difference in symptoms,” says Dr. Hanauer, who also suggests paying attention to the onset and duration of your symptoms.

Food poisoning usually comes on rapidly (often a few hours after you eat the contaminated food) and the symptoms should only last between one to three days, he says. On the flip side, stomach flu often has a slower onset because the virus needs time to infect the “host” (aka, you!), which takes one to two days. Symptoms then last between three to 10 days, says Dr. Lee.

Food poisoning vs stomach flu treatment

Unfortunately, you usually have to ride out your symptoms, regardless of whether you have food poisoning or stomach flu. This includes plenty of rest, drinking lots of fluids to make up for the loss of electrolytes, and a diet of bland foods (such as those in the BRAT diet), says Dr. Lee.

Extreme dehydration is the main concern in both cases. “During diarrhea and/or vomiting, it may be difficult to keeps foods or liquid down. Unfortunately, you may feel worse if you become dehydrated and recovery may be slowed if your body doesn’t receive the nutrients it needs,” says Jennifer Williams, MPH, a research scientist specializing in hydration at Abbott Nutrition.

“While drinking water is important for the body, it is not enough to help replace the key electrolytes, like sodium, chloride, and potassium, that are lost during dehydrating events,” says Williams. Sports drinks or other drinks that contain electrolytes, like Pedialyte, will help you recover.

Avoid raw fruits and vegetables until symptoms go away, suggests Dr. Hanauer. This includes greasy foods as well, which may be more difficult to digest. “If you have stomach flu, I usually tell patients to avoid milk products for a week. It disrupts the small intestine, where lactose (milk sugar) is absorbed, so you might not be able to absorb it until the lining of the small intestine regenerates,” he adds. “Lactose may not be a problem with bacterial food poisoning, since it affects more of the colon, not the small intestine.”

When should you see a doctor?

If you experience the following issues while dealing with your illness, it’s time to see your doctor, especially if you’re very young, very old, pregnant, have a compromised immune system, or have multiple medical issues, says Dr. Lee.

• Struggling to keep up with fluid losses with obvious signs of dehydration​
• Blood in stool
• High fever (over 101.5°F when measured orally)
• Vomiting for more than 24 hours
• Diarrhea lasting more than three days

Both food poisoning and stomach flu can result in complications, or even be fatal, if not treated properly. In severe cases, antibiotics may be necessary, says Dr. Lee. Your doctor can offer tests to determine the cause of your illness, often from a stool sample, to find the best treatment.